Arrangement for radio direction finding



March 29, 1960 CARL-ERIK GRANQVIST 2,931,037

ARRANGEMENT FOR RADIO DIRECTION FINDING Filed June 24, 1957 BY zg wATTORNEYS United States Patent F ARRANGEMENT FOR RADIO DIRECTION FINDINGCarl-Erik Granqvist, Lidingo, Sweden, assignor to Svenslra AktiebolagetGasaccumulator, Lidiugo, Sweden, a corporation of Sweden ApplicationJune 24, 1957, Seriai No. 667,316

Claims priority, application Sweden August 2, 1956 2 Claims. (Cl.343-738) The traditional way of finding direction by radio is to use astrongly directed antenna system, for instance a frame antenna, which iseither turned mechanically while observing the maximum or minimumvoltage, or the turning of which is instead simulated by connecting apair of mutually crossing antennas to a radio goniometer, the readingcoil of which being turned in a corresponding way. Both of thesearrangements, however, suffer from a disadvantage often observed. Inturnable frame antennas, which are controlled by hand, it has been usualto limit the total turning angle of the frame to a little more than oneturn. It has then been possible to connect the frame antenna with thereceiver by means of a flexible conductor without slip contacts.However, it has proved, that such a small turning is very ofteninsufficient for quick and easy handling, and by a specially expensivearrangement the total turning angle of the frame is increased up to twoturns, but thererby an expensive and complicated stop device has beennecessary, and the flexible conduits also become more complicated andexpensive. Finally this arrangement means that part of the conductor hasto hang down freely, whereby it has been sensitive to mechanicaldisturbances. Even the best ground mantled coaxial cables are to acertain degree sensitive to electro-magnetic disturbances, and thelonger the conductor is, the stronger these disturbances will be. Indirection finding with a radio goniometer one has always had to use sliprings for transferring the received signal voltage to the receiver, andthe same has been the case in automatic direction finding, whichrequires well known, continuously rotating direction finding antennas.Slip ring contacts, however, always cause disturbances due to the weakcurrents to be transferred, the so-called contact noise.

In order to avoid the above disadvantages and to provide an arrangementof a direction finding antenna, in which neither flexible conductors,nor slip ring contacts are required, it is proposed to arrange thedirection finding antenna for electromagnetic waves in such a way, thatit is influenced by the magnetic field. It contains for this purpose aturnable so-called Z-armature of a material with high conductiveproperty for this field.

In induction compasses Z-armatures have already been used, but thesehave been kept in rotation with a very high speed, whereby they induceda voltage dependent upon the horizontal component of theearth-magnetical field. In this case, thus the magnetic field isunidirectional, and the Z-armature rotates in this field for creating analternating voltage. Such an arrangement can be compared with asynchronous generator. In the arrangement according to the invention. onthe other hand, a Z-armature is used in a way, which could better becompared with the arrangement in a transformer. The armature is normallynot in rotation. but can of course be turned in two different positions.representing different directions of the input field. This, however,

is an alternating field per se, and in the winding about 2,931,637Patented Mar. 29, 1960 the stem of the Z armature therefore an electricvoltage will be created the same way as the voltage in the secondarywinding of a transformer, when the magnetic in the winding of theZ-armature then will form a measme of the direction of the input field,or in other words: The Z-armature can be used as an antenna with astrong directional action.

Tests have proved that the signal intensity achieved in this way isfully sufficient for direction finding purposes, and that this signalintensity in no way needs to be weaker than'the field intensity in anormal frame antenna device, measured as the output voltage from theantenna. On the other hand, one has fully avoided slip ring contacts aswell as long freely hanging condoctors, and thereby also all of thedisturbances occurring in all frame antenna systems, and therefore thereceived signal will be essentially more pure and easy to understand.

The said earlier known arrangement, however, is not perfect, because itis sensitive to input waves with horizontal polarization. It should beremembered, that the force lines of the input field are as a rule notonly containing an horizontal component but also a distinct verticalcomponent.

For avoiding the abovementioned disadvantages, two Z-armatures arecombined by being applied in the form of a constructive unitary part onepole contacting the other, the one Z-arrnature thereby being turned asthe image picture of the other one.

The invention will be further described below in connection with theattached drawing, which shows a form of execution of the invention.Thereby further advantages with the invention will also be mentioned. Inthe drawing Fig. 1 shows in strongly schematical form a complete systemaccording to the known form of execution, partly in block diagram. Fig.2 shows an arrange ment according to the invention for improving theantenna, provided with Z-armature.

In Fig. l a Z-armature is indicated by 10, said armature being of thekind, which is known from the induction compass techniques. The armature10 is turnable in about the same way as a normal frame antenna, about anaxis 11, which is in this case coinciding with the centre line of thestem 12 of the Z-armature. This stem is surrounded by a winding 13,which is connected with the direction finding receiver 14, shown inblock di agram, and thereby with the loudspeaker 15. On the shaft 11 ascale disc 16 with a reading mark 17 is provided. This can for instancebe provided with all kinds of different means for improving thepossibility of read ing, known from usual direction finding systems withframe antenna, such as for instance a vernier for correcting the readingangle and so on. It should, however, be observed that even if here andin the following the arrangement has been described in connection with asystem for manual direction finding, the invention is of course alsopossible to main automatic direction finding, where it will even get itsmost essential advantages.

The arrangement according to Fig. 1 functions in the following way:

When the Z-armature is directed with its one leg onto the transmittingradio beacon and with its other leg in the exactly opposite direction,the armature will receive a magnetic field, which is conducted throughthe winding 13 with the same action as if a frame antenna had beenarranged with its plane exactly perpendicular to the direction of thehorizontal component of the input wave. In a corresponding way, thearrangement according to Fig. 1 acts when the legs of the Z-armature aredirected perpendicularly to the direction of the horizontal com-'asnifra. frame .antennahadbeen. set with its level in, the ,a

direction of the input wave. The characteristic will be almost the sameas that fora frame antenna. One can consequentlyi turn; the v Z-armatureirn-the'sameway I as one used;to do in traditionalsystemsv with atrameantenna, and-listen; torthe. field intensity in the: form ofi'the sound,intensity on. an interference tonein the loudspeaker 15-. Suitably thedirection finding should, be

- made on: a minimum .ofreceivedv signalv intensity in this case as in:&i frame antenna system.

An. arrangement according to the invention for avoid ing thedisadvantages of the inclined fieldisshownin Fig; 2., I111 the:arrangement according. to. this figure, two Z=arrnatures ar.c.combined.intoj a. constructive; unit, the onecarniat ure 19' beingplaced as the image pictureyof the othnnarmaturelt); The two :coils 21,and 22, are-:connectedrjin such. a direction,. that the -voltages.created; by the; horizontal component addto each: other, whereas thevoltagesrcreated by the :vertical component-are extinguishing: eachother. In the-shown: example; the coils have been shown to: be connectedin; parallel but they could equally well have been connected in series.

Of course, this invention is not limited to the specific form ofexecution described above and shown in the drawing, but differentmodifications may occur within.

the frame of the invention.

What is claimed is:

'1. An arrangement for radio direction finding including a magneticantenna, said antenna having two magnetic cores each in the form of aZ-armature, each of said cores having a coil arranged about the stem ofsaid armature, .said cores being so arranged that one pole of each is incontact with a pole of the other, the engaging pole faces forming animaginary plane, one of said cores being turned to form the imagepicture of the other of said cores in said imaginary plane.

2. An arrangement according to claim 1, wherein said coils areconnected, whereby the voltages created by the magnetic horizontalcomponents cooperate and the voltages created by the magnetic verticalcomponents are extinguished.

References Cited in the file of this'patent UNITED STATES PATENTS2,755,468 Mountjoy July 17, 1956 we .e. 1.

